Photosynthesis Review Questions

Answer Key

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Multiple Choice:

1. E

2. B

3. D

4. A


Short answers

5. CO2 + H2O à C6H12O6 + O2

Calvin Light Calvin Light

5b. Light reaction makes ATP and NADPH (electron carriers) used by the Calvin cycle. Calvin cycle uses ATP, NADPH to build sugars. Used ADP and NADP+ from the Calvin cycle return to the light reactions to be re-energized.

6.

Sunlight excites the electrons in chlorophyll.

Electrons reduce ADP, NADP+ à ATP, NADPH

ATP, NADPH fuel formation of glucose.

7. The Calvin cycle will run out of ATP and NADPH eventually. Needs to wait for light reaction to produce more.

8. Stomata are kept closed to prevent dehydration. With closed stomata, plant can’t take in CO2 for the Calvin cycle.

9. Lots of surface area = more electron transport chains in thylakoid. Enclosed thylakoid space allows build-up of H+ concentration gradient.

10.

Graph 1: Light intensity.

Light excites electrons in chlorophyll à enzymes produce ATP, NADPH. Eventually these enzymes are working at peak speed, they cannot work any faster. (The point on the graph where rate levels off is the “saturation point”. More light does not lead to faster enzymes.)

Graph 2: Carbon dioxide

More CO2 in the Calvin cycle allows more sugar production. At saturation point, more CO2 (a substrate) will not change the rate of photosynthesis because enzymes of the Calvin cycle are already working as fast as possible.

Graph 3: Temperature.

Enzymes of photosynthesis are proteins. Too cold = less movement, fewer collisions with substrates. Too hot = enzymes denature.

11. Oxygen – carbon dioxide gas, from the atmosphere

Carbon – Carbon dioxide gas, from the atmosphere.

Hydrogen – water, from plant roots.

12. a. No. CO2 from atmosphere would be converted into organic molecules of the plant.

b. CO2 gas in the atmosphere would decrease.

13. Formed by the splitting of H2O

14. No. Light is electromagnetic energy. It is converted into chemical energy in ATP, NADPH

15. Energy requiring (synthesis)

16. Most atoms come from CO2 in the air.

17a. Yellow. Photosynthesis will produce O2.